The Bacterial Reaction Center: Where is the Center?

Abstract

The reaction center (RC) of phototrophic bacteria is responsible for primary photochemistry. It was originally described as a complex composed of three polypeptides (H, M, and L) with the following cofactors: four bacteriochloro-phylls, two bacteriopheophytins, one carotenoid, one or two quiñones, and a non heme iron (1). Subunit H can be removed from the RC without loss of photochemical activity (1,2). Recently, the characteristic absorption spectrum and its changes upon photooxidation reflecting the primary charge separation were found also in a preparation showing one single band on SDS-PAGE at the position of subunit L (3). However, this is not sufficient to prove that only one polypeptide is present in the preparation and that the band in the gel really contains subunit L. The preparation was obtained by ultrafiltration in the presence of LDAO and DOC at room temperature in the absence of protease inhibitors. Hence it may well be that breakdown products of the larger subunits comigrated in the gel with subunit L (see our results).